This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 10-2003-0011088 filed in KOREA on Feb. 21, 2003, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a duplexer filter, and more particularly, to a duplexer filter having a film bulk acoustic resonator and a semiconductor package thereof.
2. Description of the Prior Art
Generally, a film bulk acoustic resonator (FBAR) is a filter using a bulk acoustic wave of a piezoelectric layer. A size of a general frequency filter is proportional to a wavelength of an electromagnetic wave in a usage frequency band. Therefore, the size of a general frequency filter using the electromagnetic wave is relatively large. For example, when the frequency of the electromagnetic wave is 1 GHz, the size of a general frequency filter is approximately 30 cm, and when the frequency of the electromagnetic wave is 300 GHZ, the size of a general frequency filter is approximately 1 mm. However, if the bulk acoustic wave of the piezoelectric layer is used, a wavelength of the bulk acoustic wave becomes less as {fraction (1/10,000)} of a wavelength of the electromagnetic wave. According to this, the electromagnetic wave is converted into the bulk acoustic wave by the piezoelectric layer, and the size of the filter becomes less in proportion to the wavelength of the bulk acoustic wave. That is, the size of the frequency filter using the bulk acoustic wave is approximately several hundreds of microns, and a plurality of the frequency filters using the bulk acoustic wave can be fabricated at one time through a semiconductor process.
FIG. 1A is a view showing a film bulk acoustic resonator fabricated by a bulk micromachining process in accordance with the prior art.
As shown, the bulk acoustic resonator 10 fabricated by the conventional bulk micromachining process comprises: a semiconductor substrate 11 having a hole 12 formed at a lower portion by being etched by the bulk micromachining process; a film 13 formed on the semiconductor substrate 11 and covering the hole 12; a lower electrode 14 deposited on the film 13; a piezoelectric layer 15 formed on the exposed surfaces of the lower electrode 14; and an upper electrode 16 deposited on the piezoelectric layer 15.
However, when the film bulk acoustic resonator is to be fabricated by the bulk micromachining process, the semiconductor substrate 11 has to be immersed into etching solution for a long time in order to form a certain hole 12 at the semiconductor substrate 11. According to this, it takes a long time to fabricate the film bulk acoustic resonator and a damage risk is great when the film bulk acoustic resonators which have been fabricated on the semiconductor substrate are respectively separated.
FIG. 1B is a view showing a film bulk acoustic resonator fabricated by the conventional surface micromachining process in order to solve the problem of FIG. 1A.
As shown, the bulk acoustic resonator 20 fabricated by the conventional surface micromachining process comprises: a semiconductor substrate 21 having an air layer 22 formed at the upper portion thereof; a lower electrode 14 formed on the air layer 22 of the semiconductor substrate 21; a piezoelectric layer 15 formed on the exposed upper surface of the lower electrode 14; and an upper electrode 16 deposited on the piezoelectric layer 15.
The film bulk acoustic resonator fabricated by the conventional surface micromachining process is not provided with the hole 12, so that a semiconductor chip is not easily broken at the time of separation. Also, an area of the air layer 22 is not increased, so that the number of semiconductor chips per one semiconductor substrate is increased. However, in the film bulk acoustic resonator fabricated by the conventional surface micromachining process, it is very difficult to control stresses of the lower electrode 14 and the piezoelectric layer 15 positioned on the air layer 22 thereby to have a low yield rate.
FIG. 1C is a view showing a film bulk acoustic resonator fabricated by using a film bulk acoustic reflective layer 32 in accordance with the conventional art in order to solve the problem of FIG. 1B. The acoustic reflective layer 32 is called as a bragg reflector.
As shown, the film bulk acoustic resonator 30 fabricated by using the acoustic reflective layer 32 comprises: a semiconductor substrate 31; an acoustic reflective layer 32 deposited on the semiconductor substrate 31; a lower electrode 14 deposited on the acoustic reflective layer 32; a piezoelectric layer 15 formed on the exposed surfaces of the lower electrode 14; and an upper electrode 16 deposited on the piezoelectric layer 15. Herein, the acoustic reflective layer 32 is a layer formed by sequentially depositing SiO2 and W on the surface of the semiconductor substrate 31, the lower electrode 14 and the upper electrode 16 is an electrode by depositing Mo, and the piezoelectric layer 15 is a layer formed by depositing ZnO or AlN by an RF magnetron sputtering.
However, in the conventional film bulk acoustic resonators 10, 20, and 30, the lower electrode 14 formed at the semiconductor substrates 11, 21, and 31 is formed as a single layer, thereby lowering a bonding characteristic between the lower electrode 14 and the semiconductor substrates 11, 21, and 31. Also, it is difficult to extend the lower electrode 14 and the piezoelectric layer 15 having a c-axis orientation because of the influence of the semiconductor substrates 11, 21, and 31.
Hereinafter, a duplexer filter having the conventional film bulk acoustic resonator, and a plurality of passive elements such as inductors and capacitors connected to the duplexer filter will be explained with reference to FIG. 2.
FIG. 2 is a block diagram showing a duplexer filter having the conventional film bulk acoustic resonator and passive elements.
As shown, the duplexer filter 40 connected to an antenna of a mobile terminal and etc. comprises: a transmission side band-pass filter 41 and a reception side band-pass filter 42 provided with a plurality of film bulk acoustic resonators 10 connected serially and in parallel, for passing only a predetermined frequency band; and a plurality of passive elements 43 such as a plurality of inductors and capacitors connected between the transmission side band-pass filter 41 and the reception side band-pass filter 42. The reference numeral S denotes a serial connection state of the film bulk acoustic resonator, and P denotes a parallel connection state of the film bulk acoustic resonator.
Therefore, even if the transmission side band-pass filter and the reception side band-pass filter are fabricated as a size less than 1 mm×1 mm by being integrated into one semiconductor chip, passive elements such as a plurality of different inductors and capacitors are arranged at the periphery of the transmission side band-pass filter and the reception side band-pass filter. According to this, the duplexer filter actually has a size corresponding to approximately 11 mm×9 mm. Eventually, the conventional duplexer filter serves as a great obstacle in reducing a size of a mobile communication device such as a mobile terminal, and thereby a technique for integrating and packaging the conventional duplexer filter into one semiconductor chip is required.
A duplexer filter according to another conventional technique is disclosed in U.S. Pat. No. 6,559,735 which has been registered on May 6, 2003.